1. Field of the Invention
The invention in general relates to transducers, and particularly to a side looking sonar transducer which transmits acoustic energy to, or receives reflected acoustic energy from, a narrow strip on a target area such as the sea bottom.
2. Description of the Prior Art
In side looking sonar systems an elongated transducer is generally mounted on a carrier vehicle which travels either on or below the water surface along a course line. Acoustic energy is propagated in a very narrow fan shaped beam pattern toward a target area, the sea bottom, by the transducer and energy reflected from the bottom or objects on the bottom is picked up by a similar receiver transducer. As the carrier vehicle continues along its course line an indicating apparatus such as a storage tube or paper recorder, portrays a picture of the bottom in accordance with each reflected transmitted signal The resultant display is similar to a picture on a television screen in that the entire picture is made up of a plurality of parallel sweeps with each sweep being the portrayal of a reflected transmitted signal.
One type of side looking sonar transducer has been developed wherein the transducer is of a curved elongated configuration and the carrier vehicle travels at a relatively low altitude above the bottom, for example twenty feet.
The curved transducer has a radiating surface arranged on the arc of a circle whose radius is the design altitude and acoustic energy is focussed along a line of focus on the sea bottom. The curvature of the arc approximately matches the wave front curvature of the reflected acoustic energy and any variation in the design altitude results in defocussing and a consequent degradation of the display.
It is therefore an object of the present invention to provide a focussed side looking sonar transducer that provides for a greater depth of focus than transducers of the prior art.
Another type of side looking sonar transducer is the straight line configuration. This type is not focussed along a line of focus and can tolerate relatively large altitude excursions. The resolution of the desired target area relatively close to the transducer is however limited by the width of the transducer.
It is a further object to provide a straight line side looking sonar transducer that effectively increases the depth of field of the display, that is, increases the resolution for target areas relatively close to the transducer.